Angels' Share

Angels' Share

So I'm readily familiar with the idea that a portion of whisky evaporates through the wood during the aging process. I was under the impression that this "angels' share" was always more alcohol than water - in fact, the definition of "angels' share" here on WM's site specifically mentions that fact.

Reading a book on american whiskey today (The Book of Classic American Whiskeys, Waymack & Harris), I came across this passage:

Not all that happens in the barrel is easily understandable. For example, the alcoholic strength of barrels is apt to change during the aging process. In the Scotch industry, the whisky, aged in Scotland, of course, tends to lose alcoholic strength. But in the American whiskey industry, it tends to go the other way. Especially in barrels located in the upper ricks of the open warehouses, the alcoholic proof rises year by year.

What the... ? Does this mean the angels in Kentucky are more moderate in their alcohol intake?

Interestingly, the authors state there is no commonly accepted reason for the discrepancy, giving several competing theories from distillers around the area that carried very little weight - e.g., the 'osmosis theory', that water molecules are smaller than alcohol molecules and can more easily gain passage through the oak. Nice theory, but it doesn't really explain why the opposite is true in Scotland - maybe peat makes water molecules bigger? Anyway, the book is about a decade old and I was wondering if anybody had heard any sort of explanation for this phenomenon.

I don't dare stick my nose in "where Angels fear to tread"... but I think the simple explanation for the dichotomy is the temperature differences between Scotland and Kentucky (and other surrounding "hot States")... those Southern US warehouses are closer to kilns for a good part of the year, augmenting the natural evaporation - and would rarely see snow over the winter months...

I'd also guess that the another "angel" factor is related to the "liberal sampling habits" of the distillery manager and crew... and how much of a dent can be made in barrels sitting around for 10, 12 or 25+ years...

When we visited Martell Brandy in Cognac the tour guides there talk about the angels share being alcohol escaping from the barrel and it is the reason that all the buildings are a grey black colour because of a fungus grown on the buildings, as a result of the alcohol. I don't know what it proves other than in that part of France the angels share is not water.

les taylor wrote:When we visited Martell Brandy in Cognac the tour guides there talk about the angels share being alcohol escaping from the barrel and it is the reason that all the buildings are a grey black colour because of a fungus grown on the buildings, as a result of the alcohol.

You'll see that mould in Scotland around distilleries as well. This and this image show it on the warehouses. But its on bark and cars and... and...

To understand this, there are a couple of points that need to be clear up front
1) New Make averages 63,5% or higher... that means there is only 36,5% water in the solution
2) Evaporation will vary differently for alcohol and water according to temperature and moisture....meaning: variations in alcohol-evaporation will be smaller (there is no alcohol in the air, no matter what atmosferic conditions, so evaporation of alcohol will be more or less constant, but there is potentially a lot of water in the air...making evaporation of water very variable!)

this means that at certain temperatures combined with a certain humidity, water will evaporate at the same rate or faster than alcohol (in ml/min)

1) In a hot and dry climate water will evaporate at more or less the same speed as alcohol (= kentucky climate)
2) In a cold and moist climate alcohol will evaporate quicker then water (= Scotland)

Compare it to a damp cloth: If you hang it out to dry in a cold moist environment it will take a hell of a lot longer to dry than in a dry warm environment.

so given a 100l barrel:
in case 1: in 5 years time 10l of alcohol wil have evaporated and a comparable 10l of water will have evaporated....starting at 63,5%alcohol, that means that from our initial 63,5l alcohol we have 53,5l left, and from our inital 36,5l water, we have 26,5 l left.... that gives me 53,5l alcohol in 80 liters solution = appr. 66,8%Vol.... the alcoholpercentage went up!

in case 2: in 5 years time 10l alcohol but only 2l of water will have evaporated (mind you: these are just examples)....53,5l alcohol and 34,5l water in 88l solution = 60,5%vol... the alcoholpercentage went down....

Probably the chemists among us will say the above is not a 100% correct, but I think it is a more or less true and workable way to understand how the angels share can vary...

First, I have to point out that the idea of peat making water molecules bigger was a joke. My point was that it's no more absurd than the idea that the whole thing can be explained because water molecules can pass through the barrel easier because they're smaller. The rate of liquids passing through a semipermeable membrane has nothing to do with the size of a molecule of the liquid, for one thing, and for another that doesn't even address the asked question of why it's different in Scotland than in Kentucky. It's not like molecules, be they water or ethanol, vary in size based on geography (or by being 'surrounded' by peat - get it?).

Less ridiculous theories were put forth in the same book, concentrating on any number of factors: temperature, humidity, use of new casks, open warehouses, etc. They just didn't have a certain answer.

But it looks to me like the easy winner is humidity, especially since there are examples of the exact same action taking place in overly dry warehouses in Scotland (with more water than alcohol evaporating). In fact, with that knowledge isn't it a dead cinch? The drier climate explains the fact that water is evaporating faster than alcohol, while the heat explains why they lose more total volume? If it's that simple, was the book just poorly researched, or is this something that was just found out in the last few years?